1. Field of the Invention
The present invention relates to an apparatus and a method both capable of accomplishing an accurate analysis, by minimizing an intensity of the diffracted X-rays incident on the detector, in the practice of the X-ray fluorescence analysis of a sample of a kind having a crystalline structure such as, for example, a monocrystal wafer (including, for example, a monocrystal silicon wafer and a monocrystal gallium arsenide wafer), which is used in the manufacture of semiconductor electronic circuit elements, and a monitor wafer formed by depositing, for example, electrode films over an entire measuring surface of a monocrystal silicon wafer.
2. Description of Related Art
Analysis of a surface layer of, for example, a silicon wafer has hitherto been carried out by irradiating a sample surface with primary X-rays and then detecting secondary X-rays emitted from the sample surface. Where with respect to a semiconductor substrate having electric wiring films made of aluminum (Al), silicon (Si) and copper (Cu) and deposited locally on a measuring surface of the monocrystal silicon wafer, the quality of each of those wiring films, for example, the film thickness and the content concentration are to be checked, an X-ray fluorescence spectrometer is generally utilized, which spectrometer is of a type designed to irradiate a sample, in the form of a monitor wafer having the wiring films deposited over the entire measuring surface of a monocrystal silicon wafer through the same process as the semiconductor substrate, with a primary ray and then to detect and analyze secondary X-rays emitted from the sample.
The X-ray fluorescence analyzing method has been suggested in the patent document 1, listed below, in which prior to the X-ray fluorescence analysis of a sample, the sample is irradiated with primary X-rays while the sample is rotated 180 degrees about a predetermined point on the sample, secondary X-rays including fluorescent X-rays and diffracted X-rays, both emitted from the sample; the sample is repositioned at a rotational direction position at which the resultant intensity of the secondary X-rays attains the minimum value; and under this condition, the sample is moved in XY directions perpendicular to each other in a plane parallel to a measuring surface of such sample, thereby accomplishing the analysis of the entire measuring surface of the sample.
Also, the total reflection X-ray fluorescence spectrometer has been suggested in the patent document 2, similarly listed below, which includes a sample table on which a sample having a crystalline structure is fixedly placed; an X-ray source for emitting primary X-rays towards the sample; a detector on which secondary X-rays emitted from the sample are incident; a parallel translating means for moving the sample table to an arbitrarily chosen position on the sample surface so as to allow the primary X-rays to irradiate; a rotary means for rotating the sample table about an axis perpendicular to the sample surface; and a control means for controlling the rotating means so that the sample may be set within an optimum rotational angle range of the sample determined by the theoretical calculation, in which range the total intensity of diffracted X-rays diffracted by the sample and then incident on the detector attains a value lower than a predetermined value.
3. Prior Art Literature    [Patent Document 1] JP Laid-open Patent Publication No. H05-126768    [Patent Document 2] JP Laid-open Patent Publication No. H10-282022
According to the patent document 1 listed above, since in the practice of the X-ray fluorescence analyzing method disclosed, the sample having the crystalline structure that has rotational symmetries through 180 degrees is measured, after the sample has been repositioned at the angle of rotation at which the intensity of the secondary X-rays attains the minimum value and a right half region of the sample has subsequently been measured, the sample is rotated to set a left half region of the sample to a right half region, thereby allowing the entire region of the sample to be measured. It has, however, been found that in this known method, two directions such as the angle of rotation of the sample, at which the intensity of the secondary X-rays attains the minimum value, and the angle, that is 180 degrees symmetric relative to that angle, are set and, therefore, any other angle than those two angles of rotation cannot be set. For this reason, in the case of the sample having the crystalline structure that has not rotational symmetries as shown in FIG. 7, no precise analysis is accomplished because the diffracted X-rays cannot be circumvented if the measurement is performed after the right half region of the sample has been measured and the sample has then been rotated 180 degrees to set the left half region of the sample to the right half region. Also, as the circumvent angle for circumventing diffracted X-rays, the angle at which the intensity of the secondary X-rays attains the minimum value is not necessarily the optimum angle and, therefore, no precise analysis can be accomplished as well.
According to the patent document 2 listed above, in the practice of the total reflection X-ray fluorescence spectrometer disclosed therein, the sample is set by means of the theoretical calculation to the optimum rotational angle range, within which the total intensity of the diffracted X-rays attains a value lower than the predetermined value. However, it has been found that a diffraction profile, detected actually by the spectrometer, and a diffraction profile theoretically calculated do not necessarily coincide with each other and, hence, no precise analysis can be accomplished. Here a diagram, in which the angle of rotation of the sample and the intensity of the secondary X-rays emitted from the sample at that angle of rotation are correlated with each other, is referred to as a diffraction profile.